IFN-gamma is a central player in the development of psoriasis lesions, which can be involved a variety of cellular processes in the skin. Dendritic cells are important cells in driving inflammation in psoriasis through the induction of T cells that produce IL-17 in psoriasis. Injecting IFN-g into the skin can increase the numbers of T cells and also inflammatory DCs that produce cytokines involved in IL-17 production. Thus, the investigators hypothesize that the dendritic cells present in the skin after IFN-g injection polarize IL-17-producing T cells.